Keyed-taper connections, splines, bolted connections and clamped flanges give rise to fretting failure. The basis is two surfaces which are able to move relatively to each other, even by a small amount, leading to contact scars. These areas can be subjected to very high stresses which can give rise to micro cracking, and it can grow if left uncorrected.
One example was a failed shaft connected to a flange by a key and taper. After the failure the drive side of the keyway was found to have had a number of small cracks occurring at the larger end. An identical piece of equipment showed identical signs of cracking which would have to fail in due course.